The present invention relates to telecommunications apparatus
A telecommunications system normally consists of telephone cables carrying signals from the exchange to subscribers. These cables can be run in suitable conduits or suspended between telephone poles. At intervals along the cable, it is necessary to create a spur leading away from a main cable to an individual subscriber. At one time, telephone cables were almost universally suspended between telegraph poles and therefore the spur was referred to as a xe2x80x9cdrop wirexe2x80x9d. Similarly, the main cable arriving from the telephone exchange was referred to as the exchange wire.
It is necessary to create a reliable connection between the exchange wire and the drop wire, and many proposals have been made in the past as to how to do so. In particular, our earlier Patent Applications GB-A-2129630, GB-A-2176062 and EP-A-0683925 deal with suitable connection units.
It is of course necessary to test the circuit after installation and when faults are reported. The generally harsh environment of many telephone cables means that care must be taken to protect the conductive elements even during testing, and our earlier Patent Applications GB-A-2260036 and GB-A-2261773 address this problem.
A further consideration in providing test access is that telephone companies wish to avoid third parties gaining undetected access to the test points. This would enable them to tap into an existing telephone line and either eavesdrop or gain free use of the telephone system. Some telephone companies seek a xe2x80x9clook both waysxe2x80x9d capability in their test access. This refers to the ability of the engineer to break the connection at the test point and connect the test probe either to the side of the connection leading back to the exchange, or to the side leading forward to the subscriber. Thus, an independent test can be carried out of these separate circuits. Those telephone companies which require this also prefer an engineer to test the circuit to identify any signals present on that line prior to disconnection.
Our earlier EP-A-0683925 describes a modular form of apparatus, in which a permanent physical connection can be made between contacts within the unit and the exchange wire and drop wire respectively. A further discrete plug-in module can then be added to the unit to perform a variety of functions. At its simplest level, the module can provide direct interconnection between the exchange wires and drop wires. This could later be replaced for testing purposes with an open accessible connection, for example. It is expected that this modular form will become more prevalent in telecommunication systems, and therefore the present application is described in the form of a suitable module. It should however be understood that the present invention is not limited to use in such modules and could easily be applied to a larger telecommunications apparatus.
In its first aspect, the present invention addresses the difficulty of providing suitable apparatus for a variety of telecommunications companies that exist. In general, the precise requirements of each telephone company is set without reference to the other existing companies, and this means that different markets in different countries call for different specifications and equipment. The natural result of this is that the design of the particular equipment concerned must be different, and this necessitates a plurality of production lines. This means that the investment necessary to produce such products is significantly higher than would be desired.
The present invention therefore seeks to provide a telecommunications apparatus in which those components which require a significant investment cost can be used regardless of the specification laid down by the telecommunications firm. In this aspect of the invention, only parts not requiring a significant investment income need be changed in order to adapt the apparatus to a different specification.
The present invention therefore provides, in its first aspect, a telecommunications apparatus comprising an external plastics casing containing a conductive path for a telecommunications signal, and a test contact within the casing comprising an electrically conductive member, the casing including a pair of wall members and an aperture therebetween providing access to the test contact member, thereby allowing a test probe to be attached to the test contact member and one wall member thereby deflecting the test contact member from a rest position towards a test position;
the conductive path being one selected from
(a) a contiguous path adjacent the test contact member but not in contact therewith except when the latter is in a test position;
(b) a pair of conductors not in mutual contact but each in contact with the test contact member when the latter is in the rest position, one of the pair only being in contact with the test contact member when the latter is in a test position;
(c) a pair of conductors not in mutual contact but each in contact with a third conductive member when in its rest position, none of the three being in contact with the test contact member when the latter is in its rest position, deflection of the test contact member to a test position bringing it into contact with the third conductive member and causing same to be deflected from its rest position to a test position in which it is not in contact with at least one of the pair of conductors;
(d) a continuous path not in contact with the test contact member when the latter is in the rest position, which is broken when the test contact member is in the test position, one part of the path then being in contact with the test contact member.
Apparatus is therefore provided which includes the same external plastics casing and test contact member and which can be adapted to the specification required by replacement of the members forming the conductive path. These members are preferably formed of a suitable deformed metal strip, which does not require expensive or elaborate moulds.
In a preferred form of the invention, the casing includes biasing means to bias the test contact member towards its rest position. Such an arrangement provides a positive return force after the test probe is removed.
In another preferred form, the test contact member and the two walls are generally alongside each other with the test contact member between the two walls. This means that the test contact member will in use be deflected in one direction or another opposed direction, simplifying the overall construction.
The present invention also enables constructions to be prepared which are particularly advantageous in themselves. In its second aspect, the present invention therefore refers to certain such constructions in more detail.
In this second aspect, the present invention therefore provides a telecommunications apparatus including a conduction path segment from an exchange wire to a drop wire and a test port for testing that conduction path, the conduction path segment including a first and a second contact disposed within the apparatus in a non-contacting manner, the test port including a generally elongate test contact member adjacent to a wall member, the test contact member being held in a first position by at least one biasing means but deflectable therefrom to a second position on application of a test probe to the test contact member and the wall member, wherein the first and second contacts are electrically connected by a further contact when the test contact member is in the first position and are not so connected when the test contact member is in the second position.
Thus, when a test probe is connected to the line, the exchange wire and drop wire are disconnected. A third party seeking to gain unauthorised access to a telephone line will therefore be detectable In the form of a failed line. Meanwhile, an engineer is able to test the line on either the exchange wire side or the drop wire side without interference from equipment connected to the other side.
In this respect, it is preferred if there are two wall members, one either side of the test contact member, wherein the test probe can be applied to the test contact and either the first or second wall member respectively, the test contact member then being electrically connected either to the first or to the second contact according to which wall member is chosen. This allows an engineer to select which side of the circuit to test, i.e. a xe2x80x9clook both waysxe2x80x9d capability.
In one preferred form of this second aspect, the test contact member is the further contact. Thus, the first and second contacts are electrically connected via the test contact member. Displacement of the test contact member from its first position toward its second position thus disturbs this connection and breaks the connection.
In another preferred form of this aspect, the test contact member is not the further contact but is brought into contact therewith when in the second position, causing the further contact to lose its electrical contact with one of either the first or second contacts. Thus, deflection of the test contact member causes the further contact member to be displaced out of position, breaking the electrical contact between the first and second contacts.
In a preferred form of this aspect, the test probe is situated within an external case but accessible via an aperture in that casing. This serves to provide a measure of environmental protection.
In a further preferred version of all aspects, the aperture is of insufficient extent to permit a test probe to be engaged with the test contact only. This is preferably achieved by selecting a size for the test contact and for the aperture such that the test contact dimension is greater than a size which is 2 mm less than the width of the aperture. The result of this is that a test clip able to grip the test contact on either side (i.e. without deflecting it) would be of insufficient thickness to provide the necessary strength. It is therefore further preferred if the difference is less than 1.5 mm, with 1 mm being a still more preferred figure.
The aim is essentially to make the width of the aperture intermediate between the width of two jaws of the crocodile clip and those two jaws when clipped over the test contact member. Thus, only a single jaw can be fully inserted into the aperture, leaving the upper jaw to grip on the external wall adjacent the aperture. In this aspect, it is preferred if the test contact member has an enlarged head member. In a further preferred form, the aperture is sufficiently wide to allow a test probe to touch the test contact without engaging. This permits an engineer to make a temporary contact with the circuit and hence check whether it is in use prior to disconnecting it. At the same time, it prevents a permanent connection being made by a third party.
It is also preferred if the test contact member has a tapering section facing the aperture. This assists a test probe in deflecting the test contact member as it is inserted into the aperture. The included angle of the tapering section is preferably at lest twice the angle whose tangent equals the static coefficient of friction between the test contact member and the test probe.